The SOS Paradigm
The oxidant-management approaches being used during the 1980s were based largely on scientific findings, air quality models, and related air quality management tools from research conducted in southern California and the urban megalopolis in the northeastern United States. Few scientific studies had been conducted in the South. In the late 1980s, however, studies began to emerge that pointed to the South's unique air quality management problems. These problems included: 1) a high frequency of air mass stagnation, warm temperatures, high humidity, and intense solar insulation that characterize the region's summer climate; 2) abundant natural emissions of biogenic hydrocarbons from the South's ample rural and urban forests; and 3) an anthropogenic emission mix dominated by island cities and rural point sources. Because of these unique characteristics, it became apparent that air quality management approaches developed in other parts of the Nation might not be appropriate for the South. To address this concern, the Southern Oxidants Study (SOS) was formed in 1988.
The SOS is a coordinated, long-term research program focusing on the formation, accumulation, and management of photochemical oxidants in the South. Since its founding, the SOS has focused on two general purposes:
- Using the southern United States as a natural laboratory for policy-relevant scientific investigations, improving scientific and public understanding of the chemical and meteorological processes that cause ozone and other photochemical oxidants to accumulate in the atmosphere near the ground; and
- Evaluating alternative strategies by which leaders in various Federal, State, municipal, industrial, and commercial organizations can manage the accumulation of ozone and other photochemical oxidants in the atmosphere, and decrease the injurious effects of these airborne chemicals in various urban and rural areas.
Prior to the late 1980's, biogenic hydrocarbons were believed to play little or no role in ozone formation in either the rural or urban atmospheres. Two papers were pivotal in changing this viewpoint: 1) Trainer et al., (Nature, 1987) showed that biogenic hydrocarbons played a major role in rural ozone episodes in the eastern United States; and 2) Chameides et al., (Science, 1988) showed that biogenic emissions represented a significant source of volatile organic compounds (VOCs) in Atlanta and that these emissions decreased the efficacy of a VOC-based ozone abatement strategy. The findings of Trainer et al. and Chameides et al. were a major driving force behind the inception of SOS and, consequently, the study of the role of biogenic VOC in ozone formation was identified as a prominent research theme for the program.
Research conducted as part of the SOS program has been broad in scope, necessitated by the complex nature of the problem. The program participants have been responsible for significant advances in methods development, emissions characterization, model development and evaluation, and have provided important new insights into the processes that control ozone accumulation in the atmosphere (Fehsenfeld et al., 1993; Chameides and Cowling, 1995).
Field programs conducted during the early years of SOS relied primarily on ground-based measurements in the rural environment and were focused on developing a better understanding of the role of biogenic emissions in ozone formation and exploring ozone/NOY relationships. There were, however, two SOS studies that used highly instrumented aircraft to provide a more comprehensive view of regional ozone formation and transport. In each case, the instrumentation mounted on the aircraft were used to characterize the spatial variability of ozone and its precursors over the region. Further, the flight paths were designed to provide information on ozone formation in urban and power plant plumes. In 1990 an effort led by NOAA's Aeronomy Laboratory (Trainer et al., 1995) made measurements around Birmingham Alabama while in 1992 the Tennessee Valley Authority participated in a major field program in Atlanta Georgia (Imhoff et al., 1995).
The results of these studies demonstrated the extreme value of the three dimensional information provided by these kinds of platforms. The experience obtained in the conduct of these studies and the analysis of the data collected provided critical new information on ozone production efficiency in plumes and formed the basis for the Nashville/Middle Tennessee Ozone study that was conducted in 1994/1995.